1. Field of the Invention
The present invention relates to methods for producing transgenic flowering plants. In particular, this invention is directed to methods for producing transgenic poinsettia. This invention also is directed to transgenic poinsettia that express at least one macromolecule that either confers resistance to an insect pest or to a disease-causing pathogen, or otherwise enhances the commercial value of the plant.
2. Background
The poinsettia, Euphorbia pulcherrima Willd., is a member of the family Euphorbiaceae. The genus Euphorbia contains 700 to 1000 species, and is characterized by a single female flower that lacks petals and typically lacks sepals. The female flower is surrounded by individual male flowers, and the entire flower is enclosed in a cup-shaped cyathium. The red, white, yellow or pink portion of the plant, popularly referred to as the “flower,” consists of modified leaves or bracts.
Since its introduction over 170 years ago, the poinsettia has become the primary potted flowering plant produced and sold in North America. In 1996, for example, the USDA reported sales of poinsettia in the top 36 poinsettia production states of over 59 million pots, having a 214 million dollar wholesale value. Consequently, production of poinsettia potted plants is an important component of the U.S. floral industry.
Insect pests and diseases caused by pathogens can kill poinsettias even under greenhouse conditions. See, for example, Ecke, Jr., et al. (eds.), THE POINSETTIA MANUAL, 3rd Edition (Paul Ecke Publications 1990). Illustrative insect pests include whiteflies, mealybugs, thrips, aphids, and spider mites, which damage poinsettias by withdrawing plant fluids. Moreover, the larvae of fungus gnats and lepidopterous insects harm poinsettias by feeding on various plant structures.
Poinsettia are also susceptible to diseases caused by fungi and bacteria. Fungal infestation, such as Rhizoctonia root and stem rot or Pythium root and stem rot can cause a complete collapse of the poinsettia. While other fungal infections, such as poinsettia scab or Corynespora bract spot may not destroy the plant per se, the disfigurement ruins the commercial value of the infected plant. Similarly, certain bacteria, including Erwinia chrysanthemi, can kill an infected poinsettia plant, while others, such as Xanthomonas campestris pv. poinsettiaecola, destroy the plant's marketability.
Although chemical treatment can control certain of these insect pests and disease pathogens, such treatment can also have an adverse effect upon poinsettias. An alternative to chemical treatment is to genetically engineer transgenic poinsettia that express polypeptides capable of protecting the plant against the insects and pathogens. The production of transgenic plants can further be used to enhance the commercial value of poinsettia by controlling characteristics such as flower color, early flowering, day neutrality, free branching, dwarfness, fragrance, and superior post harvest and shipping qualities.
However, there has been no report to date on the successful production of transgenic poinsettia. Thus, a need still exists for a method to introduce foreign genes into poinsettia to enhance the survivability or commercial value of the plants.